add def non_user_code_prefix

[samuelcolvin]

Description

Add

def non_user_code_prefix(path: str | Path) -> None:
    if isinstance(path, Path):
        path = str(path)
    logfire._internal.stack_info.NON_USER_CODE_PREFIXES += (path,)

Equivilant to

logfire._internal.stack_info.NON_USER_CODE_PREFIXES += (str(Path(__file__).parent.absolute()),)

[samuelcolvin]

See pydantic/pydantic-ai#570, adding this to the public API, would also make it available via logfire_api.